Preconception Thyrotropin Levels and Thyroid Function at Early Gestation in Women With Hashimoto Thyroiditis.

Preconception optimization of thyroid function in women with Hashimoto thyroiditis (HT) is highly recommended to prevent/reduce the risk of thyroid insufficiency at early gestation. This work aimed to evaluate the prevalence of first-trimester thyroid insufficiency in HT women with preconception thyrotropin (T0-TSH) values consistently less than or equal to 2.5 mIU/L with or without levothyroxine (LT4) treatment, and to calculate T0-TSH cutoffs that best preconceptionally identified HT women requiring first-trimester LT4 adjustment/prescription. Serum TSH was obtained at 4- to 6-week intervals from 260 HT pregnant women (122 on LT4 [Hypo-HT]; 138 euthyroid without LT4 [Eu-HT]), prospectively followed from preconception up to pregnancy term. Receiver operating characteristic (ROC) curves were plotted to identify T0-TSH cutoffs best predicting first-trimester TSH levels greater than 2.5 mIU/L (diagnostic criterion [DC] 1) and greater than 4.0 mIU/L (DC 2). At first trimester, TSH was greater than 2.5 mIU/L in approximately 30% of both Hypo-HT and Eu-HT women, and greater than 4.0 mIU/L in 19.7% Hypo-HT and 10.1% Eu-HT women (P = .038). The optimal ROC-based T0-TSH cutoffs found were 1.24 mIU/L/1.74 mIU/L in Hypo-HT, and 1.73 mIU/L/2.07 mIU/L in Eu-HT women, for DC 1 and DC 2, respectively. T0-TSH values exceeding these cutoffs resulted in a statistically significantly increased risk of first-trimester thyroid insufficiency (odds ratio [OR] [95% CI)] 15.92 [5.06-50.15] and 16.68 [5.13-54.24] in Hypo-HT; 16.14 [6.47-40.30] and 17.36 [4.30-70.08] in Eu-HT women, for DC 1 and DC 2, respectively). The preconception TSH cutoffs that guaranteed a first-trimester TSH less than 2.5 mU/L in hypothyroid- and euthyroid-HT women were, respectively, almost 50% (1.24 mU/L) and 30% (1.73 mU/L) lower than this gestational target, and 1.74 mU/L and 2.07 mU/L in hypothyroid- and euthyroid-HT women, respectively, for a gestational target of 4.0 mU/L.

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